Detect Windows Mobile Version – Adaptation Kit Update (A.K.U.)

If you want to know which version of known Adaptation Kit Update (AKU) releases you have in your device, check out this link.

To see the AKU of your device, you can :
type : Start / Settings / System Tab / About
Using a C# application, the OSVersion.Version method returns build information.
Using the Registry : HKLM\SYSTEM\Versions\Aku

Source: Fabien Decret